1. Field of the Invention
The present invention relates to an improved process for the preparation of 3,4,5-trialkoxybenzaldehyde, and, more especially, for the preparation of 3,4,5-trimethoxybenzaldehyde from a 5-bromo-4-hydroxy-3-methoxybenzaldehyde starting material.
2. Description of the Prior Art
The most common technique in this art for the production of 3,4,5-trimethoxybenzaldehyde starting with 5-bromo-4-hydroxy-3-methoxybenzaldehyde (or 5-bromovanillin) consists in hydrolyzing the bromine atom using an aqueous sodium hydroxide solution, in the presence of copper.
After isolating the 4,5-dihydroxy-3-methoxybenzaldehyde (or 5-hydroxyvanillin) produced, the latter is methylated using dimethyl sulfate or methyl chloride.
Thus, published French Patent application No. 2,177,693 describes the methylation of 5-hydroxyvanillin by dimethyl sulfate in the presence of an alkali metal carbonate.
5-Hydroxyvanillin is itself produced by hydrolyzing 5-bromovanillin and is then extracted, especially with toluene for 47 hours, recrystallized, washed and dried.
The stage of isolating the 5-hydroxyvanillin is therefore quite lengthy and expensive. Additionally, the catalyst cannot be recovered and recycled.